ORIGINAL ARTICLE A Turn-on Fluorescent Chemosensor for Zn 2+ Based on Quinoline in Aqueous Media Yong Sung Kim 1 & Jae Jun Lee 1 & Sun Young Lee 1 & Pan-Gi Kim 2 & Cheal Kim 1 Received: 19 November 2015 /Accepted: 14 January 2016 # Springer Science+Business Media New York 2016 Abstract A simple Boff-on fluorescence type^ chemosensor 1 3-((2-(dimethylamino)ethyl)amino)-N-(quinolin-8- yl)propanamide has been synthesized for Zn 2+ . The receptor 1 comprises the quinoline moiety as fluorophore and the N,N ′ - dimethylethane-1,2-diamine as a binding site. 1 showed a re- markable fluorescence enhancement in the presence of Zn 2+ in aqueous solution. Importantly, the chemosensor 1 could be used to detect and quantify Zn 2+ in water samples. In partic- ular, this chemosensor could clearly distinguish Zn 2+ from Cd 2+ . The binding properties of 1 with Zn 2+ ions were inves- tigated by UV-vis, fluorescence, electrospray ionization mass spectroscopy and 1 H NMR titration. Keywords Fluorescence enhancement . Determination of Zn ion . Chemosensor . Quinoline Introduction Zinc is the second most abundant transition metal ion in hu- man body [1–7]. Zinc has attracted a great deal of attention [8–13], because it plays very important role in variety of physiological and pathological processes such as apoptosis, catalytic function of protein, enzyme regulation and so on [14–20]. Especially, labile Zn 2+ has been implicated in signal- ing processes in the brain, immunological function and gene transcription [21–24]. Its deficiency generates unbalanced me- tabolism, which in turn can induce retarded growth in chil- dren, brain disorders and high blood cholesterol, and also be implicated in various neurodegenerative disorders such as Alzheimer’ s disease, epilepsy, ischemic stroke, and infantile diarrhea. Excess zinc may also cause serious neurological dis- orders such as Alzheimer’ s and Parkinson’ s diseases [25–28]. Thus, a technique to detect and visualize free zinc ions would be highly demanded [29–34]. To date, many chemosensors have been reported to detect trace amount of Zn 2+ . Many of them, however, have disad- vantages such as insufficient sensitivity or selectivity, and in- hibition problems from other transition metal ions, especially Cd 2+ , which is in the same group of the periodic table and shows similar properties to Zn 2+ [35–38]. Thus, low cost and easily prepared Zn 2+ selective fluorescence chemosensors are needed for convenience [39–45]. In view of this necessity and as part of our effort devoted to zinc ion recognition, we have considered the combination of a quinoline moiety known as having desirable photo-physical properties as a fluorophore group and a N, N′-dimethyl ethyl- ene amine as a binding site (Scheme 1)[46–48]. Especially, we expected that the N, N′-dimethyl ethylene amine group, being hydrophilic in nature, would increase water-solubility of the chemosensor. Herein, we report a new chemosensor 1 for Zn 2+ , com- posed of the quinoline and N, N′-dimethyl ethylene amine moieties. We have observed its prominent fluorescence en- hancement in the presence of zinc ion, while there was no enhancement in the presence of other metal ions. In particular, it was able to distinguish Zn 2+ from Cd 2+ . Electronic supplementary material The online version of this article (doi:10.1007/s10895-016-1771-x) contains supplementary material, which is available to authorized users. * Cheal Kim chealkim@snut.ac.kr 1 Department of Fine Chemistry and Department of Interdisciplinary Bio IT Materials, Seoul National University of Science and Technology, Seoul 139-743, Republic of Korea 2 School of Ecology & Environmental Systems, Kyungpook National University, Sangju 37224, South Korea J Fluoresc DOI 10.1007/s10895-016-1771-x